Disclosed is a document illuminator using light emitting diodes in a light-transmissive element.
Document illumination systems or devices which are used for illuminating documents in order to scan, typically include an illumination source such as a tungsten lamp or fluorescent lamp and an opposing reflector. The illumination source is normally located on one side of an optical center line of the scanner under a platen or constant velocity transport (CVT) system while the reflector is positioned on the opposite side of the optical center line of the scanner under the platen or CVT system. The illumination source, in conjunction with the opposing reflector, provides illumination of the document or object being scanned by the scanner.
FIG. 1 illustrates the components of a document illumination system which may be used as a stand alone scanner or in a copier. As described in U.S. Pat. No. 6,236,470, the system may be employed in either a light lens scanning system or a digital (image input terminal) scanning system (platen or CVT) in order to illuminate a document for reproduction, display, and/or storage in an electronic memory, magnetic medium, or optical disk. The illumination system of FIG. 1 includes a platen 20 upon which a document 10 rests. The documents may be dispensed on the platen by means of a document handler 25. Document 10 is illuminated by a light source 50 which provides an active source of light to irradiate the illuminated region of the document. Typically, this source of light is provided by a linear fluorescent lamp (with or without aperture reflecting coatings 60 on the interior lamp surface to form an aperture 65), or by linear tungsten lamps. As noted above, the light source 50 is situated on one side of an optical center line 40. An imaging system (not shown) causes an image of the portion of the document immediately surrounding this optical centerline 40 to be projected onto a light sensing device such as a charge coupled device (CCD). It is known in the art that if the image is directed to a CCD sensor or a full width array sensor, the light reflected from the document about the optical centerline 40 is converted into electronic signals forming image data which electronically represent the document, and the data may be stored on a recording device such as memory storage in a computer.
On the opposite side of the optical center line 40, an opposing reflector 30 is situated. The opposing reflector 30 provides indirect illumination to the document being scanned by redirecting light which would normally not illuminate the document (light leaving the light source in a parallel or substantially parallel path with respect to the platen 20) back to the illuminated region of the document. Reflector 30 reflects scattered light 57 back 35 to the document 10 at an angle opposite from the angle of light being directly 55 emitted by the light source 50. This reflection suppresses shadowing on documents with nonplanar features.
Although illumination systems provide adequate illumination for a scanner, various problems are associated with conventional illumination systems. One such problem is the size of the lamp/reflector combination, where space can be premium. Another problem is the repair and maintenance of these relatively large illumination systems.
Further, a vast majority of document illuminators in digital input scanners are based on linear fluorescent lamps, including CCFLs (cold-cathode fluorescent lamps), which use small diameter (˜2 mm) mercury (Hg) fluorescent lamps. For high speed, high performance scanners, larger diameter (8-10 mm) xenon (Xe) linear fluorescent lamps are used in preference over larger diameter Hg linear fluorescent lamps. However, due to high voltage requirements and thermal sensitivity of the Hg lamps, as well as the desire to reduce mercury content in products, it is desirable to explore other light producing technologies such as light emitting diodes (LEDs) which may perform at high performance levels with less mechanical problems, less energy, high efficiency and less maintenance and cost. Such a side light emitting device is described by Robert S. West in U.S. Pat. No. 6,598,998. A different type of point-shaped light source is shown in US Patent Application Publication US 2002/0097578 A1 by Host Grainer. Still another line illumination device is taught in U.S. Pat. No. 6,017,130 to Tomihisa Saito, et al.
The present disclosure incorporates a small size light source in a different light-transmissive element (LTE) 100 shown in FIG. 2 below, to provide a compact document illuminator.